The present invention relates to energy storage systems suitable for use by electric utilities, factories, homes, and car propulsion systems. More particularly, the invention relates to the storage of energy in capacitors and coils suitably refrigerated for operating as superconductors.
Well over 99% of the electricity we use at present is generated at virtually the instant we use it. The rest is channeled into a few cumbersome pumped water storage systems. To keep pace with power demands that fluctuate wildly most utilities operate a multitiered system of generating equipment with newer efficient plants operating continuously and older less efficient plants and gas turbines being called up as needed. Occasionally all this equipment running at full speed cannot satisfy the demand for power. This may happen during peak summer and winter seasons when the demand for electricity exceeds the supply and brownouts occur. By the year 2000 electricity use is expected to double and without storage we can expect widespread power shortages during the hours of the day when demand from industries, offices, homes and factories is at its peak.
A few utilities already store energy by pumping water uphill to a reservoir and then using the downhill fall to generate electricity as needed, water storage being the only practical storage system available. Yet the water system is not efficient; one third of the energy used to pump the water is lost. Other experimental energy storage systems which have been investigated include hydrogen storage, chemical battery storage, compressed air storage, flywheel storage, and superconducting coils. This can all be seen in the article by D. Brand "Scientists Seek Ways of Storing Electricity to Prevent Brownouts" appearing in the July 5, 1974 issue of the Wall Street Journal.
From the discussion above it is clear that although the prior art has the potential it falls short of providing efficient low cost energy storage. The problem is that a moving current cannot be contained in the way that other energy sources, such as coal, oil, or uranium can. Once created, electricity must have somewhere to go. Thus, most experimental energy storage schemes either convert electricity generated at non-peak hours into another substance or use it to perform tasks like spinning a wheel, compressing air, pumping water, charging chemical materials and so forth. This harnessed energy can then be reproduced into electricity at periods of peak demand.
It is a well known physical fact that more energy can be stored in an inductor than in a capacitor. This is true by virtue of the fact that it is relatively easier to generate more flux (maxwells) per ampere in a coil than charge (coulombs) per volt in a capacitor. Typically, coils store one order of magnitude more energy than do capacitors. It is therefore understandable why coils find preference over capacitors in many present storage applications. However, energy storage capacity is not the only consideration for making a selection. The ease, rapidity, and accessibility of storing energy in large capacitors, despite their small energy capacity, is one of the most common and practical ways of storing energy for rapid release. The present invention seeks to preserve the practicality of using a capacitor while at the same time obtaining the benefit of the high energy storage capacity of a coil.
In capacitive energy storage systems, it is necessary to close a switch in the circuit to initiate delivery of energy in the form of current to a load. In contrast, in an inductive energy storage system, it is necessary to interrupt the current in the coil circuit to transfer the current into the load. The problem of repetitively and efficiently opening and closing the switch is non-trivial and must be considered one of the major problems in designing such systems. Furthermore, the energy which can be stored in such systems is limited. Typical storage capacities for electrostatic capacitors is about 10.sup.-3 WH/lb while magnetic coils store about 10.sup.-2 WH/lb (watt-hours/pound). By way of contrast, the lead acid battery stores about 10 WH/lb. This can all be seen in the article by C. J. Lynch "Energy Power Sources" appearing in the October 1967 issue of Science and Technology.
From the foregoing it is clear that coils store more energy than do capacitors but both fall short in practical terms in that the energy which can be stored is rather limited. One way to increase the energy storage capacity of a coil, or of a capacitor for that matter is to refrigerate the device. When this is done the metal becomes superconducting and some of the free electrons become paired together. Large scale superconducting coils have already been manufactured and indeed have achieved energy storage capacities on the order of 0.6 WH/lb. This can be seen in the article by Z. Stekly and R. Thorne "Large-Scale Applications of Superconducting Coils" appearing in the January 1973 issue of the Proceedings IEEE.
The system of the present invention stores energy in the form of electric charge which is contained within the combined electric and magnetic fields of a superconducting capacitor. The superconducting capacitor while operating at low temperature is biased at high voltage to increase its storage energy and may utilize a CCD (charge-coupled device) to obtain ease, rapidity, and accessibility for receiving, storing, and reproducing energy in the form of electric current. The system in accordance with the present invention converts electric current into electrons which can be stored in accurately defined electric and magnetic potential wells in a semiconductor. The wells can be operated in the manner of a familiar shift register moving the aggregates of charge within the semiconductor and reproducing the charge as a current as desired.
It is the purpose of the present invention to produce a high capacity, small size and low cost energy storage system for use in electric utilities, industries, homes, car propulsion systems, and factories.